List and recursion

[RehabReda]

hi guys:) i am facing a problem:-/
it is a recursive function and one of its parameters is of type list
when the function reaches its end and goes back the list won't be like the old one:?: but it will be updated with the newer on in the last function
see this code it is a code for a program to make a permutation of 5 numbers 0 1 2 3 4

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace _recursion
{
    class Program
    {
        public void recursion(List<int>history,List<int > available)
        {
            if (available.Count == 0)
            {
                for (int i = 0; i < history.Count; i++)
                {
                    Console.Write(history[i].ToString() + "->");
                }
                Console.WriteLine(" ");
                return;
            }
            for (int i = 0; i < available.Count; i++)
            {
                history.Add(available[i]);
                available.RemoveAt(i);
                recursion(history,available );

                available.Add(history[history.Count - 1]);
                 history.RemoveAt(history.Count - 1);



            }
            return;
        }
        bool[] b = new bool[5]; int [] place = new int [5];
          
        public List<int> find_available_places(List <int > available)
        {
            for (int i = 0; i < 5; i++)
            {
                place[i] = i;
            }
        
          
            for (int i = 0; i < 5; i++)
            {
                if (b[i] == false)
                {
                    available.Add(place[i]);
                }
            }
            return available;

        }
        static void Main(string[] args)
        {
           
            Program p = new Program();
            p.recursion(new List<int>(),p.find_available_places(new List<int>()));

        }
    }
}

[DdoubleD]

It's not clear by your description what you want us to do. You provided some code, and some sort of description of what it does, but not whether you want it to do something different, or you are getting an error, etc.

Please clarify how you want to be helped.

[RehabReda]

It's not clear by your description what you want us to do. You provided some code, and some sort of description of what it does, but not whether you want it to do something different, or you are getting an error, etc.

Please clarify how you want to be helped.

thanks for ur reply
the problem is that i send a list in the parameters of recursive function
how (when i reach the end of recursion and go back ) the list remains as it is first time when i was in this function

the problem is that the list will be like the last update happened no what it must be in its recursive function

[DdoubleD]

Is this program throwing an exception? I did a walkthrough and noticed you are using b[i] , but you never assign/initialize values. Also, b[i] values never get changed/updated that I can tell, so the result is always the same.

for (int i = 0; i < 5; i++)
            {
                if (b[i] == false)
                {
                    available.Add(place[i]);
                }
            }

[RehabReda]

no it didn't throw any exception

[DdoubleD]

You are stuck in and endless loop because you keep adding to "available" following the recursive call. What is the objective here?

public void recursion(List<int> history, List<int> available)
        {
            if (available.Count == 0)
            {
                for (int i = 0; i < history.Count; i++)
                {
                    Console.Write(history[i].ToString() + "->");
                }
                Console.WriteLine(" ");
                return;
            }
            for (int i = 0; i < available.Count; i++)
            {
                history.Add(available[i]);
                available.RemoveAt(i);
                recursion(history, available);

                available.Add(history[history.Count - 1]);
                history.RemoveAt(history.Count - 1);



            }
            return;
        }

[daveyb91]

You are stuck in and endless loop because you keep adding to "available" following the recursive call. What is the objective here?

public void recursion(List<int> history, List<int> available)
        {
            if (available.Count == 0)
            {
                for (int i = 0; i < history.Count; i++)
                {
                    Console.Write(history[i].ToString() + "->");
                }
                Console.WriteLine(" ");
                return;
            }
            for (int i = 0; i < available.Count; i++)
            {
                history.Add(available[i]);
                available.RemoveAt(i);
                recursion(history, available);

                available.Add(history[history.Count - 1]);
                history.RemoveAt(history.Count - 1);



            }
            return;
        }

I agree on that but, what I would like to add is, that you will never reach this bit:

available.Add(history[history.Count - 1]);
history.RemoveAt(history.Count - 1);

because you call your recursion function before these two lines are executed. So in order to fix this, you need to call your recursion function after the lines.

[DdoubleD]

I agree on that but, what I would like to add is, that you will never reach this bit:

available.Add(history[history.Count - 1]);
history.RemoveAt(history.Count - 1);

because you call your recursion function before these two lines are executed. So in order to fix this, you need to call your recursion function after the lines.

That's funny, because I stepped over those lines several times in the debugger. I'd like to hear exactly what it is that is trying to be achieved in this method because I'm not convinced those last two lines need to be there at all.

[RehabReda]

That's funny, because I stepped over those lines several times in the debugger. I'd like to hear exactly what it is that is trying to be achieved in this method because I'm not convinced those last two lines need to be there at all.

thanks alot for ur help it is working now:)

[DdoubleD]

Anytime. Please mark the thread as solved.